Mucin synthesis. III. UDP-GlcNAc:Gal beta 1-3(GlcNAc beta 1-6)GalNAc-R (GlcNAc to Gal) beta 3-N-acetylglucosaminyltransferase, an enzyme in porcine gastric mucosa involved in the elongation of mucin-type oligosaccharides

Glycosylation potential of human prostate cancer cell lines

Altered glycosylation is a universal feature of cancer cells and altered glycans can help cancer cells escape immune surveillance, facilitate tumor invasion, and increase malignancy. The goal of this study was to identify specific glycoenzymes, which could distinguish prostate cancer cells from normal prostatic cells. We investigated enzymatic activities and gene expression levels of key glycosyl- and sulfotransferases responsible for the assembly of O- and N-glycans in several prostatic cells. These cells included immortalized RWPE-1 cells derived from normal prostatic tissues, and prostate cancer cells derived from metastasis in bone (PC-3), brain (DU145), lymph node (LNCaP), and vertebra (VCaP). We found that all cells were capable of synthesizing complex N-glycans and O-glycans with the core 1 structure, and each cell line had characteristic biosynthetic pathways to modify these structures. The in vitro measured activities corresponded well to the mRNA levels of glycosyltransferases and sulfotransferases. Lectin and antibody binding to whole cells supported these results, which form the basis for the development of tumor cell-specific targeting strategies.

Glycodynamics of Mucin Biosynthesis in Gastrointestinal Tumor Cells

Glycoproteins found in the secretions and on the surfaces of cancer cells include mucins and mucin-like glycoproteins. These molecules have been shown to carry antigens that are characteristically expressed on cancer cells, including Tn and T antigens and Lewis epitopes. The structures of O-glycans are often abnormal in gastrointestinal tumors, or else are present in abnormal amounts, and these structures greatly contribute to the phenotype and biology of cancer cells. It has been shown that glycans of cancer cells have functional importance in cell adhesion, invasion and metastasis. The possible mechanisms leading to these cancer-specific changes in carbohydrate structures (termed glycodynamics) involve altered mRNA expression and catalytic activities of glycosyltransferases and sulfotransferases found in tissues and cells of gastrointestinal tumors. In a number of cases it has been possible to correlate enzyme changes with oligosaccharide structures. Different mechanisms have been suggested leading to the synthesis of cancer-specific Lewis, T and Tn antigens, but the regulation of cancer mucin antigens generally appears to be very complex and is poorly understood. The expression levels of specific mucin antigens and enzymes in gastro-intestinal tumors have diagnostic as well as prognostic value. These antigens also have potential for cancer immunotherapy. However, we first need to unravel the complexity of the control of glycosylation in cancer cells. Most importantly, studies of the functional implications of the glycodynamics in cancer cells, as related to cell adhesion and impact on the immune system will provide promising directions for future research.

Purification, characterization, and subunit structure of rat core 1 Beta1,3-galactosyltransferase

The O-linked oligosaccharides (O-glycans) in mammalian glycoproteins are classified according to their core structures. Among the most common is the core 1 disaccharide structure consisting of Galbeta1-->3GalNAcalpha1-->Ser/Thr, which is also the precursor for many extended O-glycan structures. The key enzyme for biosynthesis of core 1 O-glycan from the precursor GalNAc-alpha-Ser/Thr is UDP-Gal:GalNAc-alpha-Ser/Thr beta3-galactosyltransferase (core1 beta3-Gal-T). Core 1 beta3-Gal-T activity, which requires Mn2+, was solubilized from rat liver membranes and purified 71,034-fold to apparent homogeneity (>90% purity) in 5.7% yield by ion exchange chromatography on SP-Sepharose, affinity chromatography on immobilized asialo-bovine submaxillary mucin, and gel filtration chromatography on Superose 12. The purified enzyme is free of contaminating glycosyltransferases. Two peaks of core 1 beta3-Gal-T activity were identified in the final step on Superose 12. One peak of activity contained protein bands on non-reducing SDS-PAGE of approximately 84- and approximately 86-kDa disulfide-linked dimers, whereas the second peak of activity contained monomers of approximately 43 kDa. Reducing SDS-PAGE of these proteins gave approximately 42- and approximately 43-kDa monomers. Both the 84/86-kDa dimers and the 42/43-kDa monomers have the same novel N-terminal sequence. The purified enzyme, which is remarkably stable, has an apparent Km for UDP-Gal of 630 microm and an apparent Vmax of 206 micromol/mg/h protein using GalNAcalpha1-O-phenyl as the acceptor. The reaction product was generated using asialo-bovine submaxillary mucin as an acceptor; treatment with O-glycosidase generated the expected disaccharide Galbeta1-->3GalNAc. These studies demonstrate that activity of the core 1 beta1,3-Gal-T from rat liver is contained within a single, novel, disulfide-bonded, dimeric enzyme.

The joys of HexNAc. The synthesis and function of N- and O-glycan branches

This review covers discoveries made over the past 30-35 years that were important to our understanding of the synthetic pathway required for initiation of the antennae or branches on complex N-glycans and O-glycans. The review deals primarily with the author's contributions but the relevant work of other laboratories is also discussed. The focus of the review is almost entirely on the glycosyltransferases involved in the process. The following topics are discussed. (1) The localization of the synthesis of complex N-glycan antennae to the Golgi apparatus. (2) The "evolutionary boundary" at the stage in N-glycan processing where there is a change from oligomannose to complex N-glycans; this switch correlates with the appearance of multicellular organisms. (3) The discovery of the three enzymes which play a key role in this switch, N-acetylglucosaminyltransferases I and II and mannosidase II. (4) The "yellow brick road" which leads from oligomannose to highly branched complex N-glycans with emphasis on the enzymes involved in the process and the factors which control the routes of synthesis. (5) A short discussion of the characteristics of the enzymes involved and of the genes that encode them. (6) The role of complex N-glycans in mammalian and Caenorhabditis elegans development. (7) The crystal structure of N-acetylglucosaminyltransferase I. (8) The discovery of the enzymes which synthesize O-glycan cores 1, 2, 3 and 4 and their elongation.

Poly-N-acetyllactosamine extension in N-glycans and core 2- and core 4-branched O-glycans is differentially controlled by i-extension enzyme and different members of the beta 1,4-galactosyltransferase gene family

Poly-N-acetyllactosamines are attached to N-glycans, O-glycans, and glycolipids and serve as underlying glycans that provide functional oligosaccharides such as sialyl Lewis(X). Poly-N-acetyllactosaminyl repeats are synthesized by the alternate addition of beta1,3-linked GlcNAc and beta1,4-linked Gal by i-extension enzyme (iGnT) and a member of the beta1,4-galactosyltransferase (beta4Gal-T) gene family. In the present study, we first found that poly-N-acetyllactosamines in N-glycans are most efficiently synthesized by beta4Gal-TI and iGnT. We also found that iGnT acts less efficiently on acceptors containing increasing numbers of N-acetyllactosamine repeats, in contrast to beta4Gal-TI, which exhibits no significant change. In O-glycan biosynthesis, N-acetyllactosamine extension of core 4 branches was found to be synthesized most efficiently by iGnT and beta4Gal-TI, in contrast to core 2 branch synthesis, which requires iGnT and beta4Gal-TIV. Poly-N-acetyllactosamine extension of core 4 branches is, however, less efficient than that of N-glycans or core 2 branches. Such inefficiency is apparently due to competition between a donor substrate and acceptor in both galactosylation and N-acetylglucosaminylation, since a core 4-branched acceptor contains both Gal and GlcNAc terminals. These results, taken together, indicate that poly-N-acetyllactosamine synthesis in N-glycans and core 2- and core 4-branched O-glycans is achieved by iGnT and distinct members of the beta4Gal-T gene family. The results also exemplify intricate interactions between acceptors and specific glycosyltransferases, which play important roles in how poly-N-acetyllactosamines are synthesized in different acceptor molecules.

Pathways of O-glycan biosynthesis in cancer cells

Glycoproteins with O-glycosidically linked carbohydrate chains of complex structures and functions are found in secretions and on the cell surfaces of cancer cells. The structures of O-glycans are often unusual or abnormal in cancer, and greatly contribute to the phenotype and biology of cancer cells. Some of the mechanisms of changes in O-glycosylation pathways have been determined in cancer model systems. However, O-glycan biosynthesis is a complex process that is still poorly understood. The glycosyltransferases and sulfotransferases that synthesize O-glycans appear to exist as families of related enzymes of which individual members are expressed in a tissue- and growth-specific fashion. Studies of their regulation in cancer may reveal the connection between cancerous transformation and glycosylation which may help to understand and control the abnormal biology of tumor cells. Cancer diagnosis may be based on the appearance of certain glycosylated epitopes, and therapeutic avenues have been designed to attack cancer cells via their glycans.

High-level expression of the Neisseria meningitidis lgtA gene in Escherichia coli and characterization of the encoded N-acetylglucosaminyltransferase as a useful catalyst in the synthesis of GlcNAc beta 1-->3Gal and GalNAc beta 1-->3Gal linkages

We have expressed the Neisseria meningitidis lgtA gene at a high level in Escherichia coli. The encoded beta-N-acetylglucosaminyltransferase, referred to as LgtA, which in the bacterium is involved in the synthesis of the lacto-N-neo-tetraose structural element of the bacterial lipooligosaccharide, was obtained in an enzymatically highly active form. This glycosyltransferase appeared to be unusual in that it displays a broad acceptor specificity toward both alpha- and beta-galactosides, whether structurally related to N- or O-protein-, or lipid-linked oligosaccharides. Product analysis by one- and two-dimensional 400 MHz 1H- and 13C-NMR spectroscopy reveals that LgtA catalyzes the introduction of GlcNAc from UDP-GlcNAc in a beta 1-->3-linkage to accepting Gal residues. The enzyme can thus be characterized as a UDP-GlcNAc:Gal alpha/beta-R beta 3-N-acetylglucosaminyltransferase. Although lactose is a highly preferred acceptor substrate the recombinant enzyme also acts efficiently on monomeric and dimeric N-acetyllactosamine revealing its potential value in the synthesis of polylactosaminoglycan structures in enzyme assisted procedures. Furthermore, LgtA shows a high donor promiscuity toward UDP-GalNAc, but not toward other UDP-sugars, and can catalyze the introduction of GalNAc in beta 1-->3-linkage to alpha- or beta-Gal in the acceptor structures at moderate rates. LgtA therefore shows promise to be a useful catalyst in the preparative synthesis of both GlcNAc beta 1-->3Gal and GalNAc beta 1-->3Gal linkages.

An approach for fluorometric determination of glycosyltransferase activities

A new strategy for the fluorometric determination of glycosyltransferase activities is reported. The method involves dansyl chloride derivatization of the reduced form (pNH2phenyl) of a hydrophobic, aglycon moiety covalently linked to a number of acceptor substrates (pNO2phenyl). Focusing on the Golgi enzyme core 2 N-acetyl-glucosaminyltransferase, we found that synthesis and fractionation of the dansylated substrate derivative were rapid, easy and inexpensive. Additionally, the corresponding enzyme assay proved reproducible and very sensitive, as 0.4 pmol of reaction product were readily detected. This fluorometric approach appears therefore to be a valid tool for investigating the monitoring differential expression of glycosyltransferases exhibiting low levels of enzyme activity.

Enzyme-aided construction of medium-sized alditols of complete O-linked saccharides. The constructed hexasaccharide alditol Gal beta 1-4GlcNAc beta 1-6Gal beta 1-4GlcNAc beta 1-6(Gal beta 1-3)GalNAc-ol resists the action of endo-beta-galactosidase from Bacteroides fragilis

We have constructed by enzyme-aided in vitro synthesis a hexasaccharide alditol Gal beta 1-4GlcNAc beta 1-6Gal beta 1-4GlcNAc beta 1-6(Gal beta 1-3) GalNAc-ol and shown that it resists the action of endo-beta-galactosidase from Bacteroides fragilis under conditions where a related pentasaccharide alditol, GlcNAc beta 1-3Gal beta 1-4GlcNAc beta 1-6(Gal beta 1-3)GalNAc-ol, was completely cleaved. Together with earlier results from this laboratory, our present data imply that endo-beta-galactosidase from B. fragilis, apparently, can be used to distinguish between GlcNAc beta 1-6Gal and GlcNAc beta 1-3Gal units within linear backbone sequences of all known types of oligo-(N-acetyllactosamino)glycans.

A novel beta-N-acetylglucosaminidase activity in hog gastric mucosal microsomes: preferential hydrolysis of terminal GlcNAc beta 1-3 linkages in GlcNAc beta 1-3(GlcNAc beta 1-6)Gal beta 1-4GlcNAc, but GlcNAc beta 1-6 linkages in GlcNAc beta 1-3(GlcNAc beta 1-6)Gal

Hog gastric mucosal microsomes contain beta-N-acetylglucosaminidase activity which cleaves GlcNAc beta 1-3(GlcNAc beta 1-6)Gal beta 1-4GlcNAc at the terminal GlcNAc beta 1-3Gal linkage faster than at the GlcNAc beta 1-6Gal bond, producing mainly GlcNAc beta 1-6Gal beta 1-4GlcNAc. In a marked contrast, GlcNAc beta 1-3(GlcNAc beta 1-6)Gal is cleaved primarily at the GlcNAc beta 1-6Gal bond, while partial hydrolysis of GlcNAc beta 1-3(GlcNAc beta 1-6)Gal beta 1-4Glc reveals similar rates of cleavage for the (1-3) and (1-6) linkages. Our data support the notion that the terminal beta 1,6-linked GlcNAc unit of GlcNAc beta 1-3(GlcNAc beta 1-6)Gal beta 1-4GlcNAc may interact with the reducing end GlcNAc unit intramolecularly in water solution.

Preferred conformations and dynamics of five core structures of mucin type O-glycans determined by NMR spectroscopy and force field calculations

Glycosyltransferases acting on O-glycans have been shown to exhibit distinct specificity for the carbohydrate and the peptide moiety of their substrates. As an approach to study the 3-dimensional interactions between enzymes and O-glycan substrates, we determined the preferred conformations of five oligosaccharide-core structures of mucin type glycoproteins by NMR spectroscopy and by static and dynamic force field calculations. Seven oligosaccharides, representing five basic core structures, were investigated: Gal beta (1-3)GalNAc alpha Bzl (1, core 1), GlcNAc beta (1-6)[Gal beta (1-3)]GalNAc alpha Bzl (2, core 2), GlcNAc beta (1-3)GalNAc alpha Bzl (3, core 3), GlcNAc beta (1-6)[GlcNAc beta (1-3)]GalNAc alpha Bzl (4, core 4), GlcNAc beta (1-6)GalNAc alpha Bzl (5, core 6), the elongated core 2, Gal beta (1-4)GlcNAc beta (1-6)[Gal beta (1-3)]GalNAc alpha pNp (6) and GalNAc alpha-Bzl (7). The dynamic behaviour of the molecules was studied by Metropolis Monte Carlo (MMC) simulations. Experimental coupling constants, chemical shift changes, and NOEs were compared with results from static energy minimizations and dynamic MMC simulations and show a good agreement. MMC simulations show that the (1-6) linkage is much more flexible than the (1-3) or the (1-4) linkages. The preferred conformations of the disaccharides (1) and (3) show only slight differences due to the additional N-acetyl group in (3). The conformational equilibrium of beta (1-3) glycosidic bonds of 1 and 3 was not affected by attaching a beta (1-6) linked GlcNAc unit to the GalNAc residue in 2 and 4. However, experimental and theoretical data show that the beta (1-6) linkages of the trisaccharides 2 and 4, which carry an additional beta (1-3) linked glycosyl residue, change their preferred conformations when compared with (5). The 6-branch also shows significant interactions with the benzyl aglycon altering the preferred conformation of the hydroxymethyl group of the GalNAc to a higher proportion of the gt conformer. The (1-6) linkage of 2, 4, and 6 can have two different families of conformations of which the lower energy state is populated only to about 20% of the time whereas the other state with a relative enthalpy of approximately 4 kcal mol-1 is populated to 80%. This fact demonstrates that the two conformational states have different entropy contents. Entropy is implicitly included in MMC simulations but cannot be derived from energy minimizations.

Clinical aspects of glycoprotein biosynthesis

Glycoproteins are widely distributed among species in soluble and membrane-bound forms, associated with many different functions. The heterogenous sugar moieties of glycoproteins are assembled in the endoplasmic reticulum and in the Golgi and are implicated in many roles that require further elucidation. Glycoprotein-bound oligosaccharides show significant changes in their structures and relative occurrences during growth, development, and differentiation. Diverse alterations of these carbohydrate chains occur in diseases such as cancer, metastasis, leukemia, inflammatory, and other diseases. Structural alterations may correlate with activities of glycosyltransferases that assemble glycans, but often the biochemical origin of these changes remains unclear. This suggests a multitude of biosynthetic control mechanisms that are functional in vivo but have not yet been unraveled by in vitro studies. The multitude of carbohydrate alterations observed in disease states may not be the primary cause but may reflect the growth and biochemical activity of the affected cell. However, knowledge of the control mechanisms in the biosynthesis of glycoprotein glycans may be helpful in understanding, diagnosing, and treating disease.

Quantitation and structures of oligosaccharide chains in human trachea mucin glycoproteins

Human respiratory mucin glycoproteins from patients with cystic fibrosis were purified and oligosaccharide chains were released by treatment with alkaline borohydride. A neutral oligosaccharide alditol fraction was isolated from mucin obtained from a patient with A blood group determinant by chromatography on DEAE-cellulose and individual oligosaccharide chains were then isolated by gel filtration on BioGel P-6 columns and high performance liquid chromatography with gradient and isocratic solvent systems. The structures of the purified oligosaccharides were determined by methylation analysis, sequential glycosidase digestion and 'H-NMR spectroscopy. The amount of each chain was determined by compositional analysis. A wide array of discrete branched oligosaccharide structures that contain from 3 to 22 sugar residues were found. Many of the oligosaccharides are related and appear to be precursors of larger chains. The predominant branched oligosaccharides which accumulate contain terminal blood group H (Fuc alpha 2Ga1 beta 4) or blood group A (Fuc alpha 2(Ga1NAc alpha 3) (Ga1 beta 4) determinants which stop further branching and chain elongation. The elongation of oligosaccharide chains in respiratory mucins occurs on the beta 3-linked G1cNAc at branch points, whereas the beta 6-linked G1cNAc residue ultimately forms short side chains with a Fuc alpha 2(Ga1NAc alpha 3) Ga1 beta 4 G1cNAc beta 6 structure in individuals with A blood group determinant. The results obtained in the current studies further suggest that even higher molecular weight oligosaccharide chains with analogous branched structures are present in some human respiratory mucin glycoproteins. Increasing numbers of the repeating sequence shown in the oligosaccharide below is present in the higher molecular weight chains. [formula: see text] This data in conjunction with our earlier observations on the extensive branching of these oligosaccharide chains helps to define and explain the enormous range of oligosaccharide structures found in human and swine respiratory mucin glycoproteins. Comparison of the relative concentrations of each oligosaccharide chain suggest that these oligosaccharides represent variations of a common branched core structure which may be terminated by the addition of alpha 2-linked fucose to the beta 3/4 linked galactose residue at each branch point. These chains accumulate and are found in the highest concentrations in these respiratory mucins.

Construction of linear GlcNAc beta 1-6Gal beta 1-OR type oligosaccharides by partial cleavage of GlcNAc beta 1-3(GlcNAc beta 1-6)Gal beta 1-OR sequences with jack bean beta-N-acetylhexosaminidase

Radiolabelled GlcNAc beta 1-3(GlcNAc beta 1-6)Gal (1), GlcNAc beta 1-3)GlcNAc beta 1-6)Gal beta 1-OCH3 (4), GlcNAc beta 1-3(GlcNAc beta 1-6)Gal beta 1-4Glc (7), and GlcNAc beta 1-3(GlcNAc beta 1-6)Gal beta 1-4GlcNAc (10) were cleaved partially with jack bean beta-N-acetylhexosaminidase (EC 3.2.1.30), and the digests were analysed chromatographically. All four oligosaccharides were hydrolysed faster at the (1-6) branch, than at the (1-3) branch, but a high branch specificity was observed only with the glycan 4. The saccharides 1 and 7 resembled each other in the kinetics of the enzyme-catalysed release of their two non-reducing N-acetylglucosamine units, but the glycan 10 was rather different. The partial digestions made it possible to obtain radiolabelled GlcNAc beta 1-6Gal, GlcNAc beta 1-6Gal beta 1-OCH3, GlcNAc beta 1-6Gal beta 1-4Glc, and, in particular, GlcNAc beta 1-6Gal beta 1-4GlcNAc.

N-acetyllactosaminooligosaccharides that contain the beta-D-GlcpNAc-(1----6)-D-Gal or beta-D-GlcpNAc-(1----6)-D-GalNAc sequences reveal reduction-sensitive affinities for wheat germ agglutinin

Affinity chromatography of unreduced oligosaccharides on a small column of immobilized wheat germ agglutinin (WGA) revealed high-binding affinities for several radiolabeled molecules containing at the reducing end either beta-D-GlcpNAc-(1----6)-D-Gal, beta-D-GlcpNAc-(1----6)-beta- D-Galp-(1----4)-D-GlcNAc, beta-D-GlcpNAc-(1----6)-beta-D-Galp-(1----4)DGlc, D-GlcpNAc-(1----3)-[beta-D-GlcpNAc-(1----6)]-D-Gal, beta-D-GlcpNAc-(1----6)- D-GalNAc, or beta-D-Galp-(1----3)-[beta-D-GlcpNAc-(1----6)]-D-GalNAc sequences. Reduction changed the binding affinities remarkably: The sequences carrying a D-galactose or 2-acetamido-2-deoxy-D-galactose residue at the reducing end lost most of their affinities, but the sequences containing a D-glucose or 2-acetamido-2-deoxy-D-glucose residue at the reducing end gained additional affinity upon reduction. These findings emphasize the role of the unreduced, 6-o-substituted D-galactose and 2-acetamido-2-deoxy-D-galactose residues for the binding of saccharides to WGA, which has been recognized previously as a lectin specific for oligosaccharides containing a 2-acetamido-2-deoxy-D-glucose or sialic acid unit. The results suggested also that WGA-agarose chromatography of alditols may become a valuable method for the fractionation of oligo-N-acetyllactosaminoglycans and related saccharides.

UDP-GlcNAc: Gal beta 3GalNAc-mucin: (GlcNAc----GalNAc) beta 6-N-acetylglucosaminyltransferase and UDP-GlcNAc: Gal beta 3(GlcNAc beta 6) GalNAc-mucin (GlcNAc----Gal)beta 3-N-acetylglucosaminyltransferase from swine trachea epithelium

Two specific beta-N-acetylglucosaminyltransferases involved in the branching and elongation of mucin oligosaccharide chains, namely, a beta 1,6 N-acetylglucosaminylsaminyltransferase that transfers N-acetylglucosamine from UDP-N-acetylglucosamine to Gal beta 3GalNAc-mucin to yield Gal beta 3(GlcNAc beta 6)GalNAc-Mucin and a beta 3-N-acetylglucosaminyl transferase that transfers N-acetylglucosamine from UDP-N-acetylglucosamine to Gal beta 3(GlcNAc beta 6)GalNAc-mucin to yield GlcNAc beta 3Gal beta 3 (GlcNAc beta 6)GalNAc-Mucin were purified from the microsomal fraction of swine trachea epithelium. The beta 1,6-N-acetylglucosaminyltransferase was purified about 21,800-fold by procedures which included affinity chromatography on DEAE columns containing bound asialo Cowper's gland mucin glycoprotein with Gal beta 1,3GalNAc side chains. The apparent molecular weight estimated by gel filtration was found to be about 60 Kd. The purified enzyme showed a high specificity for Gal beta 1,3GalNAc chains and the most active substrates were mucin glycoproteins containing these chains. The apparent Km of the beta 6-glucosaminyltrans-ferase for Cowper's gland mucin glycoprotein containing Gal beta 1,3GalNAc chains was 0.53 microM; for UDP-N-acetylglucosamine, 12 microM; and for Gal beta 1,3GalNAc alpha NO2 phi, 4 mM. The activity of the beta 6-glucosaminyltransferase was dependent on the extent of glycosylation of the Gal beta 3GalNAc chains in Cowper's gland mucin glycoprotein. The best substrate for the partially purified beta 3-Glucosaminyltransferase was Cowper's gland mucin glycoprotein containing Gal beta 1,3(GlcNAc beta 6)GalNAc side chains. This enzyme showed little or no activity with intact sialylated Cowper's gland mucin glycoprotein or derivatives of this glycoprotein containing GalNAc or Gal beta 1,3GalNAc side chains. The radioactive oligosaccharides formed by these enzymes in large scale reaction mixtures were released from the mucin glycoproteins by treatment with alkaline borohydride, isolated by gel filtration on Bio-Gel P-6 and characterized by methylation analysis and sequential digestion with exoglycosidases. The oligosaccharide products formed by the beta 6- and beta 3-glucosaminyltransferases were shown to be Gal beta 3(GlcNAc beta 6) GalNAc and GlcNAc beta 3 Gal beta 3(GlcNAc beta 6)GalNAc respectively. Taken collectively, these results demonstrate that swine trachea epithelium contains two specific N-acetylglucosaminyltransferases which catalyze the initial branching and elongation reactions involved in the synthesis of O-linked oligosaccharide chains in respiratory mucin glycoproteins. The first enzyme a beta 6-glucosaminyltransferase converts Gal beta 3GalNAc chains in mucin glycoproteins to Gal beta 3(GlcNAc beta 6)GalNAc chains.(ABSTRACT TRUNCATED AT 400 WORDS)

Separation by liquid chromatography (under elevated pressure) of benzyl and nitrophenyl glycosides of oligosaccharides

Liquid chromatography under elevated pressure (l.c.) was employed for the separation of some benzyl and nitrophenyl glycosides of a variety of mono-, di-, tri-, and tetra-saccharides. The separation was conducted on a Waters Carbohydrate Analysis column by use of a mixture of acetonitrile-water as the mobile phase. In general, monosaccharides emerged first from the column, followed sequentially by di-, tri-, and tetra-saccharides. It was observed that the pattern of substitution imparts a noticeable effect on the elution profiles of isomeric oligosaccharides. Also, substitution of a hydroxyl group with a methyl group, or its replacement with a fluorine atom, led to a substantial decrease in retention times of some oligosaccharides. Moreover, resolution was clearly enhanced, and retention times were congruently increased by decreasing the water content of the mobile phase.

Synthetic mucin fragments. Benzyl O-(2-acetamido-2-deoxy-alpha-D-glucopyranosyl)-(1----3)-O-beta-D- galactopyranosyl-(1----3)-O-[(2-acetamido-2-deoxy-beta-D-glucopyran osy l)- (1----6)]-2-acetamido-2-deoxy-alpha-D-galactopyranoside and benzyl O-(2-acetamido-2-deoxy-beta-D-glucopyranosyl)-(1----3)-O-beta-D- galactopyranosyl-(1----3)-O-[beta-D-galactopyranosyl-(1----6)]-2-ac eta mido- 2-deoxy-alpha-D-galactopyranoside

Treatment of benzyl 2-acetamido-2-deoxy-alpha-D-galactopyranoside with 4-methoxybenzaldehyde dimethyl acetal in N,N-dimethylformamide in the presence of 4-toluenesulfonic acid afforded the 4,6-O-(4-methoxybenzylidene) acetal, which was glycosylated with 2,3,4,6-tetra-O-acetyl-alpha-D-galactopyranosyl bromide (1). Reductive ring-opening of the acetal group provided a 6-O-(4-methoxybenzyl) derivative (4) which was glycosylated with 1, followed by removal of the 4-methoxybenzyl ether group, to give benzyl 2-acetamido-2-deoxy-3,4-di-O-(2,3,4,6-tetra-O-acetyl-beta-D-galactopyran osyl)- alpha-D-galactopyranoside (7). The disaccharide diol 5, obtained from 4, and benzyl O-(2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-beta-D-glucopyranosyl-(1----3) -O- (2,4,6-tri-O-acetyl-beta-D-galactopyranosyl)-(1----3)-2-acetamido-2-deox y- alpha-D-galactopyranoside (11) were similarly glycosylated with 1 to afford a trisaccharide derivative 9 and a tetrasaccharide derivative 14, respectively. Diol 11 was also condensed with 2-methyl-(3,4,6-tri-O-acetyl-1,2-di-deoxy-alpha-D-glucopyrano)-[2, 1-d]-2- oxazoline to give a tetrasaccharide derivative 16. O-Deacetylation of trisaccharides 7 and 9, and tetrasaccharides 14 and 16 furnished trisaccharides 8 and 10, and the title tetrasaccharides 15 and 17, respectively. The structures of compounds 8, 10, 15, and 17 were established by 13C-n.m.r. spectroscopy.

Biosynthesis of polylactosaminoglycans. Novikoff ascites tumor cells contain two UDP-GlcNAc:beta-galactoside beta 1----6-N-acetylglucosaminyltransferase activities

Novikoff ascites tumor cells contain a UDP-GlcNAc:beta-galactoside beta 1----6-N-acetylglucosaminyltransferase (beta 6-GlcNAc-transferase B) that acts on galactosides and N-acetylgalactosaminides in which the accepting sugar is beta 1----3 substituted by a Gal or GlcNAc residue. Characterization of enzyme products by 1H-NMR and methylation analysis indicates that an R beta 1----3(GlcNAc beta 1----6)Gal- branching point is formed such as occurs in blood-group-I-active substances. The enzyme does not show an absolute divalent cation requirement and 20 mM EDTA is not inhibitory. The activity is strongly inhibited by Triton X-100 at concentrations of greater than or equal to 0.2%. Competition studies suggest that a single enzyme acts on Gal beta 1----3Gal beta 1----4Glc, GlcNAc beta 1----3Gal beta 1----4GlcNAc and GlcNAc beta 1----3GalNAc alpha-O-benzyl (Km values 0.71, 0.83 and 0.53 mM, respectively). Gal beta----3Gal beta 1----4Glc as an acceptor substrate for beta 6-GlcNAc-transferase B does not inhibit the incorporation of GlcNAc in beta 1----6 linkage to the terminal Gal residues of asialo-alpha 1-acid glycoprotein catalyzed by a beta-galactoside beta 1----6-N-acetylglucosaminyltransferase (beta 6-GlcNAc-transferase A) previously described in Novikoff ascites tumor cells [D. H. Van den Eijnden, H. Winterwerp, P. Smeeman & W.E.C.M. Schiphorst (1983) J. Biol. Chem. 258, 3435-3437]. Neither is Triton X-100 at a concentration of 0.8% inhibitory for the activity of beta 6-GlcNAc-transferase A. This activity is absent from hog gastric mucosa microsomes, which has been described to contain high levels of beta 6-GlcNAc-transferase B. [F. Piller, J. P. Cartron, A. Maranduba, A. Veyrières, Y. Leroy & B. Fournet (1984) J. Biol. Chem. 259, 13,385-13,390]. Our results show that Novikoff tumor cells contain two beta-galactoside beta 6-GlcNAc-transferases, which differ in acceptor specificity and tolerance towards Triton X-100. A role for these enzymes in the synthesis of branched polylactosaminoglycans and of O-linked oligosaccharide core structures having blood-group I activity is proposed.

Mucin synthesis. Conversion of R1-beta 1-3Gal-R2 to R1-beta 1-3(GlcNAc beta 1-6)Gal-R2 and of R1-beta 1-3GalNAc-R2 to R1-beta 1-3(GlcNAc beta 1-6)GalNAc-R2 by a beta 6-N-acetylglucosaminyltransferase in pig gastric mucosa

A UDP-GlcNAc:R1-beta 1-3Gal(NAc)-R2 [GlcNAc to Gal(NAc)] beta 6-N-acetylglucosaminyltransferase activity from pig gastric mucosa microsomes catalyzes the formation of GlcNAc beta 1-3(GlcNAc beta 1-6)Gal-R from GlcNAc beta 1-3Gal-R where -R is -beta 1-3GalNAc-alpha-benzyl or -beta 1-3(GlcNAc beta 1-6)GalNAc-alpha-benzyl. This enzyme is therefore involved in the synthesis of the I antigenic determinant in mucin-type oligosaccharides. The enzyme also converts Gal beta 1-3Gal beta 1-4Glc to Gal beta 1-3(GlcNAc beta 1-6)Gal beta 1-4Glc. The enzyme was stimulated by Triton X-100 at concentrations between 0 and 0.2% and was inhibited by Triton X-100 at 0.5%. There is no requirement for Mn2+ and the enzyme activity is reduced to 65% in the presence of 10 mM EDTA. Enzyme products were purified and identified by proton NMR, methylation analysis and beta-galactosidase digestion. Competition studies suggest that this pig gastric mucosal beta 6-GlcNAc-transferase activity is due to the same enzyme that converts Gal beta 1-3GalNAc-R to mucin core 2, Gal beta 1-3(GlcNAc beta 1-6)GalNAc-R, and GlcNAc beta 1-3GalNAc-R to mucin core 4, GlcNAc beta 1-3(GlcNAc beta 1-6)GalNAc-R. Substrate specificity studies indicate that the enzyme attaches GlcNAc to either Gal or GalNAc in beta (1-6) linkage, provided these residues are substituted in beta (1-3) linkage by either GlcNAc or Gal. The insertion of a GlcNAc beta 1-3 residue into Gal beta 1-3GalNAc-R to form GlcNAc beta 1-3Gal beta 1-3GalNAc-R prevents insertion of GlcNAc into GalNAc. These studies establish several novel pathways in mucin-type oligosaccharide biosynthesis.

N-acetyl-beta-D-glucosaminyltransferases related to the synthesis of mucin-type glycoproteins in human ovarian tissue

The presence of N-acetyl-beta-D-glucosaminyltransferases in microsome preparations from human ovarian tissues was investigated with UDP-GlcNAc and several synthetic oligosaccharides as acceptors. The products were identified by paper chromatography and the linkage of the 2-acetamido-2-deoxy-beta-D-glucopyranosyl group incorporated into oligosaccharides was determined by exoglycosidase digestions, 1H-n.m.r. spectroscopy, and methylation analysis. These results showed that ovarian microsome preparations contain both beta-(1----3)- and beta-(1----6)-N-acetyl-D-glucosaminyltransferase activities which might be involved in the synthesis of mucin-type glycoproteins. Substrate competition tests suggested that both UDP-GlcNAc:-Bn glycoside of beta-D-GlcpNAc-(1----6)-alpha-D-GalpNAc [GlcNAc to GalNAc] and -Bn glycoside of beta-D-Galp-(1----3)-[beta-D-GlcNAc-(1----6)]-alpha-D-GalpNAc [GlcNAc to Gal] beta-(1----3)-N-acetyl-D-glucosaminyltransferase activities reside in a single enzyme species.

Biosynthesis of bloodgroup I and i antigens. A sensitive and specific assay of UDP-GlcNAc:beta-galactoside beta 1----3-N-acetylglucosaminyltransferase activity in hematopoietic cells by HPLC

A sensitive HPLC method for the assay of UDP-GlcNAc:beta-galactoside beta 1----3-N-acetylglucosaminyltransferase activity was developed. Using lactose as an acceptor, the formation of the product GlcNAc beta 1----3Gal beta 1----4Glc can be determined without interference by substrates resulting from enzymatic and chemical breakdown of the donor substrate UDP-GlcNAc. The method is very specific since products of other transferase reactions, which potentially may be formed in the incubations in vitro, elute at positions different from that of GlcNAc beta 1----3Gal beta 1----4Glc. By use of this assay method it could be demonstrated that normal and malignant hematopoietic cells and cell-lines, with the exception of erythrocytes and reticulocytes, contain beta 1----3-N-acetylglucosaminyltransferase activity.

Mucin biosynthesis. Properties of a bovine tracheal mucin beta-6-N-acetylglucosaminyltransferase

We have characterized a bovine tracheal mucin beta-6-N-acetylglucosaminyltransferase that catalyses the transfer of N-acetylglucosamine from UDP-N-acetylglucosamine to the C-6 of the N-acetylgalactosamine residue of galactosyl-beta 1----3-N-acetylgalactosamine. Optimal enzyme activity was obtained between pH 7.5-8.5, at 5mM-MnCl2, and at 0.06-0.08% (v/v) Triton X-100 (or Nonidet P-40), or 0.5-5.0% (v/v) Tween 20. Ba2+, Mg2+ and Ca2+ could partially replace Mn2+, but Co2+, Fe2+, Cd2+ and Zn2+ could not. Sodium dodecyl sulphate, cetylpyridinium chloride, sodium deoxycholate, octyl beta-D-glucoside, digitonin and alkyl alcohols were less effective in enhancing enzyme activity, and dimethyl sulphoxide was ineffective. The apparent Michaelis constants were 1.25 mM for UDP-N-acetylglucosamine, 0.94-3.34 mM for freezing-point-depressing glycoprotein and 0.19 mM for periodate-treated blood-group-A porcine submaxillary mucin. Asialo ovine submaxillary mucin could not serve as the glycosyl acceptor. The structure of the 14C-labelled oligosaccharide obtained by alkaline-borohydride treatment of the product was identified as Gal beta 1----3(Glc-NAc beta 1----6)N-acetylgalactosaminitol by beta-hexosaminidase treatment, gas chromatography-mass spectrometry and 1H-n.m.r. (270 MHz) analysis. The enzyme is important in the regulation of mucin oligosaccharide biosynthesis.

Mucin synthesis. UDP-GlcNAc:GalNAc-R beta 3-N-acetylglucosaminyltransferase and UDP-GlcNAc:GlcNAc beta 1-3GalNAc-R (GlcNAc to GalNAc) beta 6-N-acetylglucosaminyltransferase from pig and rat colon mucosa

Pig and rat colon mucosal membrane preparations catalyze the in vitro transfer of N-acetyl-D-glucosamine (GlcNAc) from UDP-GlcNAc to GalNAc-ovine submaxillary mucin to form GlcNAc beta 1-3GalNAc-mucin. Rat colon also catalyzes the in vitro transfer of GlcNAc from UDP-GlcNAc to GlcNAc beta 1-3GalNAc-mucin to form GlcNAc beta 1-3(GlcNAc beta 1-6) GalNAc-mucin. This is the first demonstration of in vitro synthesis of the GlcNAc beta 1-3GalNAc disaccharide and of the GlcNAc beta 1-3-(GlcNAc beta 1-6)GalNAc trisaccharide, two of the four major core types found in mammalian glycoproteins of the mucin type, i.e., those containing oligosaccharides with GalNAc-alpha-serine (threonine) linkages. The activity catalyzing synthesis of the disaccharide has been named UDP-GlcNAc:GalNAc-R beta 3-N-acetylglucosaminyltransferase (mucin core 3 beta 3-GlcNAc-transferase), while the activity responsible for synthesizing the trisaccharide has been named UDP-GlcNAc:GlcNAc beta 1-3GalNAc-R (GlcNAc to GalNAc) beta 6-N-acetylglucosaminyltransferase (mucin core 4 beta 6-GlcNAc-transferase). The beta 3-GlcNAc-transferase from pig colon is activated by Triton X-100, has an absolute requirement for Mn2+, and transfers GlcNAc to GalNAc-alpha-phenyl, GalNAc-alpha-benzyl, and GalNAc-ovine submaxillary mucin with apparent Km values of 5, 2, and 3 mM and Vmax values of 59, 62, and 37 nmol h-1 (mg of protein)-1, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Synthesis of benzyl 2-acetamido-2-deoxy-3-O-beta-D-fucopyranosyl-alpha-D-galactopyranoside and benzyl 2-acetamido-6-O-(2-acetamido-2-deoxy-beta- D-glucopyranosyl)-2-deoxy-3-O-beta-D-fucopyranosyl-alpha-D- galactopyranoside

Condensation of benzyl 2-acetamido-4,6-O-benzylidene-2-deoxy-alpha-D- galactopyranoside with 2,3,4-tri-O-acetyl-alpha-D-fucopyranosyl bromide in 1:1 nitromethane-benzene, in the presence of powdered mercuric cyanide, afforded benzyl 2-acetamido-4,6-O-benzylidene-2-deoxy-3-O-(2,3,4-tri-O-acetyl-beta-D- fucopyranosyl)-alpha-D-galactopyranoside (3). Cleavage of the benzylidene group of 3 with hot, 60% aqueous acetic acid afforded diol 4, which, on deacetylation, furnished the disaccharide 5. Condensation of diol 4 with 2-methyl-(3,4,6-tri-O-acetyl-1,2-di-deoxy-alpha-D-glucopyrano)-[2, 1-d]-2- oxazoline in 1,2-dichloroethane afforded the trisaccharide derivative (7). Deacetylation of 7 with Amberlyst A-26 (OH-) anion-exchange resin in methanol gave the title trisaccharide (8). The structures of 5 and 8 were confirmed by 13C-n.m.r. spectroscopy.